Part 2: Ignitable Liquids: Petroleum Distillates, Petroleum Products, and Other Stuff

Presented by:
Dr. John DeHaan

For those investigators still wondering where the term "ignitable liquid" came from, there is a much bigger change in the world of petroleum products that is now very much a part of our world of fire debris analysis and interpretation. Time was when petroleum products of the types encountered in fire scenes (and their related debris) fell into a few neat categories. Most frequently encountered was good old gasoline (which fortunately for us in North America was a complex mixture of aromatic (benzene-like) compounds and aliphatic (saturated straight-chain) hydrocarbons that was unique (not found in any other product) and nearly unchangeable from place-to-place and year-to-year (except for seasonal variations such as winter-blend or high-altitude formulations). Kerosene was the next most-common accelerant (even more so than gasoline in some parts of the U.S.) ­ a true petroleum distillate with a very predictable and very stable formulation, whose gas chromatographic peak profile made it easily identifiable. Paint thinners, lamp oils, camping fuels, and the like rounded out the list of petroleum distillates encountered. Other petroleum products such as blends like lacquer thinners, enamel reducers, and specialty solvents or single-compound liquids like acetone or methyl alcohol pretty well took care of anything we encountered as a potential accelerant. Few consumer products contained any such products (or if they did, they were at such low levels that our lab methods did not reveal them). We could recognize the pyrolysis products of wood, carpet, carpet pad, upholstery materials and distinguish them from petroleum product accelerants by simple pattern recognition of the meager collection of peaks that we used to consider good chromatographic separation.

The first hint of trouble was in the late 1970s when a breed of isoparaffinic (branched hydrocarbon) solvents showed up as copier toner. Well, that was OK because it was a very distinctive pattern of peaks (even if it did not have the characteristic regular "major peaks" of true petroleum distillates) and the pattern did not conflict with that of any other product. We were not likely to encounter it as an "accelerant" anyway except in schools or offices where a copier might be used.*1 By the early 1980s, the situation seemed so stable that when ATF started teaching arson accelerant detection to criminalists from all over the U.S., it was clear that a codified scheme for classifying these materials was workable. This scheme was intended to improve communication between arson analysts and make it possible to organize reference collections and data banks of chromatograms. This scheme was originally: light petroleum distillates (LPD's), medium petroleum distillates (MPD's), heavy petroleum distillates (HPD's), gasolines, and others. It served those of us in the forensic science community very well. When it was used as the basis for the ASTM Standard Practice E1387, it was expanded, refined, and given numbers and examples, as below:

Class 1: Light Petroleum Distillates, C4 to C8 hydrocarbons. Rubber cement thinners.

Class 2: Gasoline, C4 ­ C12 + specific aromatic compounds. All gasolines incl. white gas (camping fuel) and aviation gas.

Class 3: Medium petroleum distillates, C8 ­ C13 n-alkanes. Paint thinners, torch fuels.

Class 4: Heavy petroleum distillates, C9 ­ C17. Kerosene, fuel oil #1, jet fuels.

Class 5: Heavy petroleum distillates, C9 ­ C23. Diesel fuel, fuel oil #2.

Class 0: Others: Single compounds, special blended products, oxygenates (ketones and alcohols), isoparaffinics, etc.

Since 95 percent or more of the possible accelerants detected in fire debris cases fell into the first five classes, this scheme was found to be very practical. There were arguments that splitting heavy petroleum distillates into two categories was kind of artificial. Then some analysts discovered that newer passive methods of extraction such as charcoal strip did not readily pick up the C17 to C23 compounds, and therefore, misclassifications could result. This created pressure to do away with the split HPD classification. There was also confusion among analysts as to whether the classes referred to true petroleum distillates alone (which was the original intent of the authors) or to any petroleum products that fell into the boiling point ranges listed. Because it took fewer keystrokes or less time or whatever, some analysts started using the Class numbers in reports to describe their findings. It took a while before feedback from users of the reports (investigators, judges, prosecutors, and even consultant petroleum chemists) made it clear that those numbers had no meaning in the real world outside the forensic lab. (No one outside the lab had ever heard of a Class 3 petroleum distillate!) Maybe it was the cachet of using a bit of jargon that was entirely the province of the lab analysts, but one way or another, confusion, not communication, was resulting.

But the world outside the forensic labs and fire investigators was changing, in particular, the world of petroleum chemistry was changing, and this would force far more significant changes. The isoparaffinic solvent once used only as a copier toner had a distinct advantage that it had the same solvent properties as some true distillates but it did not have the characteristic odor that many people found objectionable. This spawned a whole gamut of isoparaffinic products with boiling point ranges from very light (C7 ­C10 range) to quite heavy (C17+). They found uses in consumer products from shoe polishes to insecticides. They were also easy to create in the petroleum refinery, Cycloalkanes (predominately cyclopentane, cyclohexane, and cycloheptane and their related compounds) found similar uses and a variety of products called "naphthenics" started shoeing up as charcoal starters, lamp oils, and kersosene substitutes. (If you buy "kerosene" in bulk today for use in your room heater, chances are it is an isoparaffinic product and not a "kerosene class" petroleum distillate at all). Such products could be used as fuels because of their high hydrogen content without the double bonds and benzene bonds found in aromatics that cause soot formation.

Next, and most problematic for arson debris analysts, was the development of aromatic compounds (benzene and naphthalene rings with any number of additions and substitutions) that have excellent solvent properties for products such as insecticides and adhesives. They can also disperse in water to form dilutions for spray applications. Many of these aromatic blends are readily distinguishable by pattern recognition of their GC peak patterns but some contain exactly the same aromatics that we used to see only in automotive gasoline. Like many of the heavier isoparaffinic products, these aromatic blends were not readily distinguishable from pyrolysis products on the basis of simple GC peak patterns of n-alkanes as landmarks.

None of these "new" petroleum products are true distillates, they are extracts and "creations" of the petroleum engineers gluing bits and pieces of hydrocarbon molecules from the refinery waste stream together to make useful, salable products. (We used to joke in Chicago that Armour Packaging used all of the pig but the squeal - today's petroleum chemist seemingly uses all of the petroleum crude but the traces of methane, and turns all of it into profit, er, product.) Many of us agreed that the original classification scheme was intended only for the classification of true petroleum distillates and that all the other belonged in the "Other Category." But it was becoming clear that GC/MS was needed to help identify most of the new products. By the early 1990's there was as many "Other" products as there were traditional products as there were traditional distillates. The scheme was revised to include sub-classes of the "Other" category: Isoparaffinics, oxygenates, aromatics, naphthenics, etc. Such sub-categories had little connection to the real world and a description of a volatile residue as a "class 0.3 Isoparaffinic" did little to help the investigator.

Compounding the problem were improvements in the resolution and sensitivity of the GC and GC/MS systems in use in forensic labs and a dramatic increase in the sensitivity of the techniques used for the extraction or isolation of volatiles from the fire debris. Suddenly, 1ppm or better, detection levels were being reported and lab analysts were seeing petroleum product residues in all kinds of products- new athletic shoes, tile cements, carpet backings, and many more. *2 Some of these were the very same "new" products that were causing complications for the revised E1387 scheme, and they were coming in light, medium, and heavy boiling point ranges. So now what?

As of March 2002, a new classification scheme will be part of ASTM E-1618. (See Chart A)

Examples of each category will be included in the table with instructions that these examples be included in the reported results. Note that numbers are no longer used as a major reference and that each description can be more complete and (it is hoped), more useful to the investigator when reading labels on suspected comparison samples. More product labels are including more specific descriptors such as: aromatic products or isoparaffinic solvents, etc. Note also that there are no longer a destinction of heavy petroleum distillates between diesel fuel and kerosene. It is hoped that the distinction will still be made by the analyst and reported to the user, This new scheme reflects changing consumer uses and products and a much-changed petroleum refining process, as well as improved sensitivity and discrimination of the lab methods used. There is also a desire to provide the investigator with the most accurate and meaningful (useful) information. The investigator must strive to understand what there product designations mean and use that information to evaluate various accidental and intentional sources of such residues in fire debris. If all else fails (or if in doubt), collect comparison samples of all potential accelerants and contaminants at the scene (preferably in their original containers) and submit them along with the questioned samples and let the lab sort them out!

1. More about the role of accelerants in a future column.
2. More about the increase in sensitivity in extraction and analysis in a future column.
3. More about comparison samples in a future column, too.

P.S.: "Ignitable liquids" is a term used when referring to both flammable liquids (Flash point below 100F)

About the author:

Dr. John DeHaan has been a criminalist for some 32 years. He has worked at county, State, and Federal forensic labs. He is a native of Chicago and his Bachelor of Science degree in physics was from the University of Illinois at Chicago. He has been involved with fire and explosion investigations for over 30 years, and has authored dozens of papers on fires, explosions, and their investigation and analysis. He is probably best known as the author of the textbook Kirk's Fire Investigation (now in its Fourth Edition). His doctorate (in 1995), from the University of Strathclyde in Glasgow, Scotland, was on the Reconstruction of Fires Involving Flammable Liquids.

He is a member of NFPA, and served on its 921 Technical Committee from 1991-1999. He is a member of the IAAI and serves on its Forensic Science Committee. He holds a diploma in Fire Investigation from the Forensic Science Society (United Kingdom) and one from the Institution of Fire Engineers (U.K.). He is a Fellow of the American Board of Criminalistics in Fire Debris Analysis and a member of the Institution of Fire Engineers. He retired from the California Department of Justice in December 1998 and is now the president of his own consulting firm, Fire-Ex Forensics, Inc., Based in Vallejo, California, where he now serves as a consultant in fire and explosion cases all over the U.S., Canada and overseas.

Other articles in the Our Changing World Series

• Our Changing World: Fires, Fuels, Investigations, and Investigators
• Our Changing World Part 2: Ignitable Liquids: Petroleum Distillates, Petroleum Products, and Other Stuff
• Our Changing World Part 3: Detection Limits: Is More Sensitive Necessarily Better?
• Our Changing World Part 4: A Matter of Time